1) Field of the Invention
The present invention relates generally to method and apparatus for reducing the visual blur of an object (particularly elements of a display) being viewed by an observer experiencing vibration. More particularly, stroboscopic image modulation is used to reduce the visual blur due to effects of the vibration.
2) Description of Related Art
When an object is experiencing vibration, an observer trying to focus on the object may see a blurred image of the object. This becomes particularly problematic when the perceived object is a display having text or characters that the observer needs to read or focus particular attention on. It is known in the art that illuminating an object (experiencing vibration) with a strobe light can decrease the perceived blur of the object for a stationary observer, if the light is strobed at or near the frequency (or integer factors [divisors] of) of the vibration.
U.S. Pat. No. 4,167,877 by Avery discloses the use of a strobe and accelerometer to analyze the resonant frequency(s) of a structure.
U.S. Pat. No. 5,591,972 by Noble et al, discloses strobing LED(s) at a predetermined frequency to read optical information from a distant object.
For situations where the observer is experiencing vibration and the object is stationary, or both the observer and object are experiencing vibration, the situation is more complex. When a vibrating object is viewed by a stationary observer, certain biological eye-movement mechanisms help the observer compensate for the shifting position of the viewed object. “Smooth pursuit” movements help to keep the image of a moving object on the foveal region of the retina. Saccadic eye movements help to rapidly shift the line of sight between successive points of fixation. When an observer is experiencing vibration, (in particular the observer's head), additional biological eye-movement mechanisms come into play. Vibration that cause rotation of the observer's head can trigger the vestibulo-ocular reflex, which in turn results in rotation of the eyes seeking to maintain an object's image on the foveal region of the retina. In addition the optokinetic reflex is triggered to assist the vestibulo-ocular reflex. If the object being viewed is shifting in position (near to far, or vice versa) due to relative motion between the observer and the viewed object, vergence eye movements (that coordinate rotations of the eyes for accurate binocular imaging) can come into play. For low temporal frequencies, all of these mechanisms help to mitigate the effects of observer vibration. However, these mechanisms are unable to accurately track higher temporal frequencies, and in fact can exacerbate the detrimental effects of vibration on human vision.